As is well known by those skilled in the art, a continuing goal in manufacturing and production of semiconductors is a reduction in size of components and circuits with the concurrent result of an increase in the number of circuits and/or circuit elements such as transistors, capacitors, etc., on a single semiconductor device. This relentless and successful reduction in size of the circuit elements has also required reduction in the size of the conductive lines connecting devices and circuits. However, as the conducting lines are designed to be smaller and smaller, the resistance of the interconnects increases.
In the past, aluminum was used as the metal interconnect lines and silicon oxide as the dielectric. However, newer manufacturing techniques now favor copper as the metal for interconnect lines and various low-k materials (organic and inorganic) are favored as the dielectric material. Not surprisingly, these material changes have required changes in the processing methods. In particular, because of the difficulty of etching copper without also causing unacceptable damage to the dielectric material, the technique of forming the metal interconnect lines has experienced significant changes. Namely, whereas aluminum interconnects could be formed by depositing a layer of aluminum and then using photoresist, lithography, and etching to leave a desired pattern of aluminum lines, the formation of copper interconnect lines are typically formed by a process now commonly referred to as a damascene or dual damascene process. The damascene process is almost the reverse of etching, and simply stated, an aperture such as a trench, canal or via is cut, etched or otherwise formed in the underlying dielectric and is then filled with metal (i.e., copper).
Unfortunately, although copper has the advantages discussed above, it readily diffuses into dielectric material used in the manufacture of semiconductor devices. Diffusion of copper into the dielectric materials of a semiconductor deice can cause serious reliability problems including electrical shorts. Therefore, it is typical to form a diffusion barrier layer between the copper used for conductors and leads and the dielectric material of a semiconductor device. Typical barrier layers may be formed of refractory metals and nitrides of these metals. Some examples of prior art barrier layers include Ta (tantalum), TaN (tantalum nitride), Ti (titanium), TiN (titanium nitride) and various combinations of these metals as well as other metal. The diffusion barrier layer is typically formed on the bottom and sidewalls of the trenches and vias of the copper interconnects to prevent the copper from diffusing into the surrounding silicon dioxide as other dielectric material. In addition, according to the prior art a capping layer of a suitable material, such as silicon nitride, could be deposited as a cover layer over the complete structure including the conductor areas and the dielectric layer before another layer or level of dielectric structure was deposited.
Unfortunately, the traditional diffusion barrier materials have poor adhesion to copper and may peel away thereby creating poor interface properties including a path for copper to diffuse into the subsequent or cover layer of dielectric material. The same path may also allow moisture and contaminants to diffuse from outside into the copper so as to form porous copper oxide. In addition, these barrier materials also create high electrical resistance at small geometrics such as below 300 Å.
U.S. Pat. No. 6,541,136 issued to Kwan, et al. and entitled “Superconducting Structure” discusses superconducting structures that include “rare earth-barium-copper oxide, and especially yttrium-barrier-copper oxide.”
U.S. Pat. No. 5,629,268 issued to Tanaka, et al., and entitled “Process for Preparing a Layered Superconducting Structure” also discusses the preparation of a layered superconducting structure based on material that includes barium copper oxide combined with rare earth elements including yttrium.
U.S. Pat. No. 6,518,648 issued to Lopatin and entitled Superconductor Barrier Layer for Integrated Circuit Interconnects provides an integrated circuit that includes a high temperature semiconductor material such as yttrium barium copper oxide as a barrier layer.